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Stray Voltage and
Electrical Safety Problems Go Hand-in-Hand
Stray voltage is a small voltage difference between two animal contact points. In dairy barns, this is often called a cow- contact point. A common example is a small voltage difference between the water cup and the floor of a dairy barn. When the animal touches both surfaces, completing the electrical circuit, a small current flows through its body. Elevated voltages across cow-contact points are called "stray" because they are not present under normal conditions. When voltages across cow-contact points are significant the production losses can be substantial. Fortunately, most dairy farms in Minnesota do not have problems with stray voltage. When stray voltage problems do occur the sources can be found and corrected as a result of a thorough investigation using the proper equipment.
Symptoms of stray voltage
Production losses are the result of animals altering their behavior because of the small shocks or tingles associated with high cow-contact voltages. These voltages are not large enough to harm the animal. If dangerous levels of voltage are present then a safety problem exists, and should be corrected immediately by a licensed electrician. Some of the changes in animal behavior are: (1) cows are excessively nervous during milking (dancing around in the stall); (2) cows are reluctant to enter the parlor or stall; (3) cows are reluctant to use waterers or to consume feed; and (4) poor milk letdown. Dairy producers should remember that these changes in animal behavior can also occur due to problems with milking equipment, changes in milking routine, spoilage of feed, or pollution of drinking water. Therefore, all potential sources of behavioral changes should be investigated. For more detailed information on the effects of stray voltage on dairy cows ask your county extension agent for a copy of the following extension bulletin:
Causes of stray voltage
Sources of stray voltage can be from
on-farm and off-farm sources. Off-farm sources of stray voltage can be related to primary
neutral-to-earth voltages, and can be dealt with by your electric utility. Common on-farm
sources of stray voltage on dairy farms are: worn insulation on wiring, loose wiring connections,
improper use of equipment grounds, electrical shorts, unbalanced 120 volt loads, and improper
installation of electric fences or cow trainers. All of these sources of stray voltage
can be corrected. Finding and correcting sources of stray voltage requires a complete
investigation by qualified professionals using the proper equipment.
Improper grounding is a safety problem
Proper use of grounding wires on electrical equipment is required in all buildings. However, this is a common oversight on many farms. Improper grounding is not only a cause of stray voltage, but it is also a safety hazard. As long as all of the electrical equipment is in good condition then an improperly grounded system will work. However, if a motor or heating element fails then a person or an animal could receive a fatal shock due to improper grounding of the system. Such a condition is not a stray voltage problem (even though it can cause stray voltage), but is a safety problem. It should be corrected immediately. If a producer routinely feels shocks while operating electrical equipment or by touching metal in any type of livestock building then a grounding problem may exist.
What should be done if a stray voltage or safety problem is suspected?
If a stray voltage problem is suspected begin the problem solving process by taking all of the following actions -- do not delay.
On some farms it may be necessary for electric utility personnel to install an isolating device to reduce the stray voltage level. However, any electrical safety hazards should also be corrected. The complex electrical systems of dairy facilities sometimes need special attention to provide a safe and productive environment for the cows and the operators.
If you suspect that you have a grounding problem then have a licensed electrician inspect the wiring on your farm to determine if it meets all requirements for livestock buildings. Use the Farm Buildings Wiring Handbook (MWPS-28) as a guide. Make all necessary wiring corrections.
What measures can be taken to prevent stray voltage and safety problems in new livestock buildings and milking centers?
Make sure that all new livestock buildings and milking centers are wired according to the special requirements given in the National Electric Code (Article 547). Have the wiring properly inspected. Some insurance companies may require that all wiring meets code specifications for livestock buildings. Others may give a reduction in premiums if code requirements are met. In new milking parlors, installation of an equipotential plane and voltage ramp is highly recommended. An equipotential plane is created when the reinforcing steel in the concrete floor is electrically bonded to all metal equipment in the milking parlor. The complete system is grounded at the service entrance panel. A properly installed equipotential plane will maintain all floor surfaces and equipment in the parlor at the same voltage. As a result, no voltage difference can occur across cow-contact points. A properly installed equipotential plane will provide the greatest insurance against future stray voltage problems in milking parlors. The specifications for the proper installation of an equipotential plane and voltage ramp are given in the Farm Buildings Wiring Handbook.
University of Minnesota,
U. S. Department of Agriculture, and Minnesota Counties Cooperating
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